Various fabric reinforced modified bitumen or asphalt products have been used in the past as membranes on residential and commercial roofing. Typically the modified bitumen is used with suitable polymeric and/or fiber glass reinforcing mats, felts, or scrims to produce a sheet product which is used as the roofing membrane.
The disadvantage with these asphalt roofing products, though, is that their commercial success is dwindling because many jurisdictions have adopted tough and stringent building code regulations to which building materials such as roofing membranes must conform. These stringent building codes have been adopted because of the increasing amount of deaths and property damage which result each year from fires. Not surprisingly, as part of their criterion the stringent building codes are demanding that roofing materials meet the Class A requirement of the UL 790 or ASTM E-108 Tests which are essentially the same. The flame spread is a measure of the ability of the asphalt composition to retard the spread of flame subsequent to being ignited. A Class A material is one which has a flame spread (i.e., burn length) of no more than about 6 feet.
Since the existing asphalt based roofing membranes have been unable to meet the stringent Class A requirements, attempts have been made to modify the existing products. The most common procedure has been to flood coat a sheet material with asphalt and then coat the surface of the asphalt impregnated sheet with fine stone or gravel, the idea being that the gravel helps to retard the spread of flame.
This procedure is disadvantageous, though, for several reasons. To begin with, the procedure is labor intensive and time consuming. The final product is rather unattractive for commercial purposes and its weight is increased by the addition of the stone. Finally, the product does not char well which is disadvantageous since char creates an insulating layer which helps to block fire penetration.
What is needed in the industry is an asphalt based material which is suitable for use as a simple to construct, light weight, roof material and which meets the increasingly stringent fire code requirements as measured according to UL 790 or ASTM E-108.